The present invention pertains to a machine tool for workpiece machining, including triaxial machining of workpieces and more particularly to a machine tool with at least one machining unit, which has at least one work spindle which can be rotatably driven around an axis of rotation, provided with a revolver head that has a plurality of driven spindles, which carry a tool in a tool carrier each and are displaceable in a work space in the X, Y and Z directions and with at least one tool magazine arranged in the work space.
A machine tool of this type with a revolver head and a tool magazine arranged in the work space, which has the features noted above, is shown in EP 433 248 A2.
Machine tools with a revolver head makes possible a rapid tool change by simple rotation of the revolver head. However, the number of tools arranged on a revolver head is usually limited to eight tools. It is common practice for repetition work, e.g., in so-called CNC-controlled machining centers, to replace the tools in one operation manually when all eight tools arranged on the tool revolver have become worn or otherwise unfit for use. Even though the number of available tools can be increased by using a plurality of tool revolvers in the case of the use of multi-station machine tools, this is, of course much more complicated and expensive.
A machine tool with a revolver head for mounting tools with a coaxial drum magazine for storing additional tools and with an automatic means for delivering the tools from the magazine into a working position at the revolver head has been known from DE 27 37 225 A1, where a separate lifting means for transporting the tools from and to the drum magazine is provided in the revolver head. This additional lifting means as well as the concentrically arranged drum magazine proper require relatively much space. In addition, displaceability of the revolver head in the X, Y and Z directions is not provided here.
Another machine tool with automatic tool change is described in DE-OS 14 77 429, in which the tool spindle and the tool magazine are arranged on a common carriage and the magazine holds the tools by means of the spindle at right angles to the spindle axis. A separate gripper-type change mechanism is likewise provided for the tool change here, where the gripper first removes the tools from the magazine in the direction of the spindle axis, then pivots them into the spindle axis and finally pushes them again into the spindle. This type of tool change is also complicated and time-consuming.
A hydraulic clamping device for the detachable precision holding of machine parts, which is also called a hydraulic expansion clamping device, has been known from EP 890 402 A1. This has axially parallel, especially cylindrical holding surfaces with wall parts which can be bent out elastically, which define a hollow space, which is connected to at least one hydraulic pressure source. The pressure source comprises a piston, which is moved by a manually actuated hexagon socket screw arranged in a threaded hole of the housing. Automatic adjustment of the hexagon socket screw is not provided for here and would also lead to increased wear and, because of the complicated coupling of the screwing tool, to a slowdown of the tool change process.
The basic object of the present invention is therefore to provide a machine tool of this type that makes possible a rapid, automatic tool change between the tool carrier on the spindle and a tool magazine within the work space.
According to the present invention, the tool carriers of the spindle and of the tool magazine are arranged in the work space for the tool change and are preferably moved from their longitudinal direction from one tool carrier into the other tool carrier by means of an actuating means arranged at the tool magazine, which preferably comprises only a lifting cylinder and a guide sleeve. A precision tool carrier, which comprises a hydraulic expansion chuck according to the present invention and makes possible a very high accuracy of fit, is arranged according to the present invention at the spindle.
One peculiarity is that the individual tools do not have intermediate holders of their own, with which the tools are usually accurately positioned at the tool spindle. The tools are moved according to the present invention without intermediate holder between the magazine and the spindle. The elimination of the so-called intermediate holder is made possible by the fact that the spindle of the revolver head can be positioned exactly at the tool carrier of the tool magazine and the tool shank can be pushed in a correctly fitting manner into the tool carrier of the spindle preferably with a simple change slide.
Furthermore, provisions are made according to the present invention for the hydraulic expansion chuck to be clamped and released automatically by means of the spindle. To do so, a ring, which actuates at least one linearly movable hydraulic piston to change the pressure of the hydraulic expansion chuck, is rotatably movable on the tool carrier of the spindle. To actuate the hydraulic piston, the ring performs a movement relative to the tool carrier of the spindle by the spindle being rotated with the tool carrier and the ring being fixed on the tool carrier of the tool magazine by means of a rotation prevention device. The drive of the spindle is thus used in a simple manner to change the pressure of the hydraulic medium by means of the hydraulic piston and to release or clamp the hydraulic expansion chuck. The tool change can consequently be performed automatically and within a very short time and without manual intervention in the closed work space.
To change the pressure in the hydraulic space, it proved to be favorable to push the hydraulic piston to the outside by spring force, on the one hand, and to move it inward against the spring force by actuating the ring, on the other hand.
The ring arranged rotatably movably on the tool carrier may consist of a threaded ring or a tensioning nut and be moved in a defined manner in the axial direction by its rotary movement relative to the tool carrier and to also one or more hydraulic pistons in the axial direction, which ensure a change in the pressure at the hydraulic expansion chuck. Instead of a threaded ring, which can be moved axially continuously and over any desired number of revolutions, it is also possible to use an eccentric ring, which can move the hydraulic piston toward the center of the hydraulic expansion chuck during a rotary movement by, e.g., 90xc2x0. As an alternative to this, the releasing and clamping of the hydraulic expansion chuck may also be brought about by means of a slot on the chuck and changer housing. The hydraulic piston is preferably arranged radially in this case, but it may also be directed inwardly at any desired oblique angle.
The use of the hydraulic expansion chuck has the advantage that the tools can be mounted without clearance with a very high repeating accuracy of approx. 0.002 mm.
The tool magazine is designed especially as a round magazine with a central axis of rotation and a rotating drive belonging to it, wherein preferably four or five tool carriers are arranged on a common bridge axially in parallel, distributed over the circumference, with an actuating device acting in the direction of the axis of rotation acting centrally on the bridge. This actuating device, which is expediently designed as a lifting or hydraulic cylinder, has a change slide, which is mounted displaceably on guide elements fastened to the housing. This change slide is directly connected to the central lifting cylinder and via the bridge to the tool carriers arranged distributed over the circumference. The bridge extends at right angles to the axis of rotation of the tool magazine and has arms which extend to the outside in a star-shaped pattern and on which at least two gripping arms and/or plate springs each, which are laterally in contact with the tool under pretension are fastened for mounting the tools. In addition, guide elements, which extend axially in parallel to the axis of rotation of the tool carriers, are guided in the arms of the bridge for displacing the tool carriers during the tool change. Compression springs, which act against the actuating device and with which the tools arranged in the tool carriers of the magazine are pressed into the housing of the tool magazine, are arranged at the guide elements. For tool change, the tools are then pressed from the housing into the tool carriers of the spindle on the revolver head by means of the central lifting cylinder against the force of the compression spring. Consequently, the tool is held by the compression springs in the tool magazine and is protected there by the housing from contamination and mechanical damage, on the one hand, and, on the other hand, it is pushed into the hydraulic expansion chuck on the spindle in an accurately fitting manner by a well-defined force applied by the lifting cylinder.
Consequently, preferably four or five tools can be additionally automatically removed from the tool magazine one after another besides the, e.g., eight tools arranged on the revolver head by means of this tool change device by a short and rapid displacement of the revolver head and by a defined movement of the lifting cylinder arranged in the tool magazine. The tool magazine can then be displaced and/or pivoted around a tilt axis from a change position (see FIG. 1) into a resting position (see FIG. 2) outside the outer contour of the tools arranged on the revolver head. The work process is therefore not hindered by the tool magazine which can be displaced in the work space with the revolver head.
As an alternative to the round magazine, the tool magazine may also be designed as a cog strip with tool carriers arranged next to one another, which is displaceable with the revolver head. However, both the tool magazines designed as round magazines and the tool magazines designed as cog strips may also be fastened on one or more sides on the machine column, in which case the spindle is brought into the change position before the tool carrier of the tool magazine for the tool change.
The features and advantages of the tool change device according to the present invention, e.g., for a multispindle two-station CNC machining center, can be summed up as follows:
1. Only the lips of the tools are changed. As a result, it is possible to use especially lightweight tools with a small space requirement and, on the other hand, a large number of tools can be accommodated in the tool magazine in a small space.
2. The tools are changed directly into the revolver with short setting-up time and the tool change is performed automatically and without the intervention of the operating personnel.
3. The tool shank is of a cylindrical design and the chips can be stripped off from the tool shank during the introduction of the tools by means of guide sleeves designed as stripping rings. High accuracy of centering is reached by eliminating holes in the clamping diameter.
4. The precision tool carrier on the spindle has a fluid-actuated hydraulic expansion chuck. Mounting of the tool without clearance is possible as a result.
5. A plurality of tools located in parallel to one another can be deposited on the magazines and the tool change is possible by a simple rotary and/or translatory movement.
6. Two stripping rings are fastened to the round magazine. Precentering of the spindle is possible by means of the outer ring and chip particles are stripped off by the movement of the first ring on the tool shank.
7. If needed, a plurality of revolvers with associated tool magazines can be accommodated in the work space and the individual magazines can be replaced as well.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.